The present invention relates generally to sockets that accept packaged integrated circuits, and more specifically to sockets that accept pin grid array packages.
As integrated circuits become larger and faster, they also become harder to test and debug in end-user systems. When an end-user system is undergoing debug, it can be convenient to monitor electrical signals on integrated circuit package pins. Modem integrated circuit packages, however, often have pins numbered in the hundreds or thousands, and gaining physical or electrical access to pins can be difficult. One known mechanism for gaining access to integrated circuit package pins in an end-user system includes the use of an interposer beneath the integrated circuit. One such interposer is shown in FIG. 1.
FIG. 1 shows a side view of an interposer between an integrated circuit package and a socket. Socket 104 is attached to printed circuit board (PCB) 106, interposer 122 is attached to socket 104, and integrated circuit package 102 is attached to interposer 122. Interposer 122 is included between integrated circuit package 102 and socket 104 to facilitate testing and debug. Typically, interposer 122 includes signal traces coupled to the pins of integrated circuit package 102. The signal traces are brought out away from the rest of the assembly to allow access by test equipment such as logic analyzers and oscilloscopes.
Socket 104 is typically a zero insertion force (ZIF) socket or a low insertion force (LIF) socket such as those available from the AMP division of Tyco International Inc., and from Foxconn Electronics Inc.
In the assembly shown in FIG. 1, with interposer 122 in place, integrated circuit package 102 is distance 108 from PCB 106. A portion of this distance is attributable to the height of interposer 122. When interposer 122 is not in place, integrated circuit package 102 is coupled directly to either socket 104 or PCB 106. It can be seen that the addition of interposer 122 increases the distance between integrated circuit package 102 and PCB 106. This increased distance influences the length of signal lines, and also causes integrated circuit package 102 to protrude further from PCB 106. In very high speed systems, it can be detrimental to signal quality to increase the length of signal lines, and in some mechanically crowded systems, it may not be possible to allow integrated circuit package 102 to protrude far from PCB 106.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for improved mechanisms to access integrated circuit package pins.